The invention relates to an apparatus for applying adhesive to the outside surfaces of book blocks to be encased in book casings inside a casing-in machine. Such an apparatus includes an adhesive application device with two application rollers which are positioned opposite each other in the adhesive-application area, wherein each roller rolls off one outside surface of a book block that is conveyed on a saddle plate of a circulating conveyor. The adhesive application rollers are provided with a recess that forms a shoulder parallel to the rotational axis and is used to apply adhesive to the fold region of a book block. The rotational position of the recess can be adjusted and changed based on the position of a specific fold on a book block conveyed through the adhesive-application area. The speed of the conveyor for the saddle plates and the rotational movement of the application rollers, which cooperate with the latter, are synchronized.
Until the present, a considerable expenditure in equipment was necessary in a casing-in machine for adjusting the adhesive-application rollers relative to the book block. According to European patent document EP 1 072 435 A1, a traction mechanism is provided for an infinitely variable adjustment of the relative position between saddle plate and/or conveyor and the rotational position of the application rollers. Among other things, this type of arrangement has the disadvantage that adhesive can be applied only according to a fixed pattern since the position of the conveyor relative to the adhesive application device cannot be changed.
The present invention takes a different approach by providing an apparatus of the aforementioned type with structural measures for optimizing the orientation of the adhesive-application rollers, relative to the book block that is passing through, thereby resulting in a better quality and higher reliability. Product-dependent variables must be taken into consideration for this, for example, the book block thickness, the shape of the book block spine, and/or the paper quality.